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Please use this guide instead, this one was written in a hurry and I forgot I had the older one.

Basically, you'll want to start with the MCP 1.12 release (temporarily at ), and then modify it to work with 1.12.2. This is actually quite simple. First, you need to edit conf/version.cfg and set both versions to 1.12.2. That on its own is not enough, but it's a critical step. Then you need to grab new SRG mappings. Normally you'd get that through the !srg command, but MCPBot doesn't have it for some versions. Instead, you can get it through forge's maven. (normally it's also on the export site but not for 1.12.2). The link is . To set that up, first delete the conf/patches folder (otherwise patches will be merged, breaking things), and then unzip the contents of that ZIP into conf, overwriting files as prompted. Then, grab a fresh set of MCP mappings. You can get this just via the export site: . Grab the latest fields, methods, and params CSV files, and place those in conf as well. That's all! You can now run the normal MCP scripts, and it'll work for that version.

Note that as always, the MCP license applies, even for development builds.  Please read the LICENSE.txt included with MCP for more information about what you are and are not permitted to do.

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ghost commented Oct 15, 2017

that dident work):

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xiphmont commented Nov 24, 2017

Thanks, worked perfectly.

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Ghent commented Dec 13, 2017

Worked great for me, thank you!

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stevex86-old commented Dec 23, 2017

One more thing that you may have to do if you're the Eclipse project or importing into another IDE – the Eclipse project configuration adds the 1.12 jar, 1.12 natives, and Realms dependencies to the classpath. Due to the discrepancies in version you have to modify the classpath to reflect the proper versions per 1.12.2:

e.g. in eclipse/Client/.classpath

<classpathentry kind="lib" path="jars/versions/1.12.2/1.12.2.jar">
		<attribute name="org.eclipse.jdt.launching.CLASSPATH_ATTR_LIBRARY_PATH_ENTRY" value="Client/jars/versions/1.12.2/1.12.2-natives"/>
<classpathentry kind="lib" path="jars/libraries/com/mojang/realms/1.10.17/realms-1.10.17.jar"/>

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gurland commented Feb 27, 2018

Thanks! It works

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orborb commented Mar 28, 2018

When I try to decompile, it just says:

Traceback (most recent call last):
File "runtime\", line 61, in decompile
commands = Commands(conffile, verify=True, no_patch=no_patch, workdir=workdir, json=json)
File "E:\DarkSun\runtime\", line 178, in init
normalStart = self.readconf(workdir, json)
File "E:\DarkSun\runtime\", line 491, in readconf
self.versionClient, self.versionServer = self.getVersions()
TypeError: 'NoneType' object is not iterable

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Dyiing commented May 31, 2018

Works as expected, many thanks.

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hYdos commented Jul 20, 2018

can u do a 1.13 guide plz im making a custom server jar and need the src code

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max0782YT commented May 11, 2021

When i try to debug, says:
Exception in thread "main" java.lang.UnsatisfiedLinkError: no lwjgl64 in java.library.path: C:\Users\User.p2\pool\plugins\org.eclipse.justj.openjdk.hotspot.jre.full.win32.x86_64_15.0.2.v20210201-0955\jre\bin;C:\WINDOWS\Sun\Java\bin;C:\WINDOWS\system32;C:\WINDOWS;C:/Users/User/.p2/pool/plugins/org.eclipse.justj.openjdk.hotspot.jre.full.win32.x86_64_15.0.2.v20210201-0955/jre/bin/server;C:/Users/User/.p2/pool/plugins/org.eclipse.justj.openjdk.hotspot.jre.full.win32.x86_64_15.0.2.v20210201-0955/jre/bin;C:\Program Files (x86)\Common Files\Oracle\Java\javapath;C:\ProgramData\Oracle\Java\javapath;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0;C:\WINDOWS\System32\OpenSSH;C:\Program Files\NVIDIA Corporation\NVIDIA NvDLISR;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\Program Files\Java\jdk-13.0.2;C:\Program Files\Java\jdk-13.0.2\bin;C:\Program Files\dotnet;C:\Program Files\Microsoft SQL Server\130\Tools\Binn;C:\Program Files\Microsoft SQL Server\Client SDK\ODBC\170\Tools\Binn;C:\Program Files\Java\jdk-16;C:\Program Files\Java\jdk-16\bin;C:\Program Files (x86)\IVI Foundation\VISA\WinNT\Bin;C:\Users\User.p2\pool\plugins\org.eclipse.justj.openjdk.hotspot.jre.full.win32.x86_64_15.0.2.v20210201-0955\jre\bin;C:\Users\User\AppData\Local\Microsoft\WindowsApps;C:\Users\User.dotnet\tools;C:\Users\User\AppData\Local\GitHubDesktop\bin;C:\WINDOWS\System32;;.
at java.base/java.lang.ClassLoader.loadLibrary(
at java.base/java.lang.Runtime.loadLibrary0(
at java.base/java.lang.System.loadLibrary(
at org.lwjgl.Sys$
at java.base/
at org.lwjgl.Sys.doLoadLibrary(
at org.lwjgl.Sys.loadLibrary(
at org.lwjgl.Sys.(
at net.minecraft.client.Minecraft.getSystemTime(
at net.minecraft.client.main.Main.main(
at Start.main(

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